Diffusion barrier layer for mems devices

ABSTRACT

Described herein is the use of a diffusion barrier layer between metallic layers in MEMS devices. The diffusion barrier layer prevents mixing of the two metals, which can alter desired physical characteristics and complicate processing. In one example, the diffusion barrier layer may be used as part of a movable reflective structure in interferometric modulators.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/614,311, filed Nov. 6, 2009, now U.S. Pat. No. 8,085,458 issued onDec. 27, 2011, which is a divisional of U.S. patent application Ser. No.11/261,236, filed Oct. 28, 2005, now U.S. Pat. No. 7,630,114 issued Dec.8, 2009, and assigned to the assignee hereof. The disclosure of each ofthe prior applications is considered part of, and is incorporated byreference in, this disclosure.

FIELD OF THE INVENTION

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY OF THE INVENTION

One embodiment disclosed herein includes a MEMS device, comprising amechanical membrane, wherein the membrane includes a first metalliclayer, a second metallic layer and a diffusion barrier layer positionedbetween the first metallic layer and the second metallic layer, whereinthe diffusion barrier layer is adapted to substantially inhibit anyportion of the first metallic layer from mixing with any portion of thesecond metallic layer.

Another embodiment disclosed herein includes a method of substantiallyinhibiting any portion of a first metallic layer from mixing with anyportion of a second metallic layer in a MEMS device mechanical membrane,comprising positioning a diffusion barrier layer between the first andsecond metallic layers.

Another embodiment disclosed herein includes a method of manufacturing aMEMS device, including depositing a first metallic layer, depositing adiffusion barrier layer onto the first metallic layer, depositing asecond metallic layer onto the diffusion barrier layer, wherein thediffusion barrier layer is adapted to substantially inhibit any portionof the first metallic layer from mixing with any portion of the secondmetallic layer, and etching a same pattern in the first metallic layer,diffusion barrier layer, and second metallic layer.

Another embodiment disclosed herein includes a MEMS device, having amechanical membrane produced by the above process.

Another embodiment disclosed herein includes an interferometricmodulator, comprising a movable reflective layer that includes a mirror,a mechanical layer adjacent to the mirror, the mechanical layer adaptedto provide mechanical support for the mirror, and a diffusion barrierbetween the mirror and the mechanical layer, wherein the diffusionbarrier is adapted to substantially inhibit mixing of any portion of themirror with any portion of the mechanical layer.

Another embodiment disclosed herein includes an interferometricmodulator, comprising a movable reflective layer that includesreflecting means for reflecting light, mechanical support means forproviding mechanical support to the reflecting means, and diffusionbarrier means for preventing diffusion between the reflecting means andthe mechanical support means.

Another embodiment disclosed herein includes a method of manufacturingan interferometric modulator, including depositing a first metalliclayer, depositing a diffusion barrier layer onto the first metalliclayer, depositing a second metallic layer onto the diffusion barrierlayer, wherein the diffusion barrier layer is adapted to substantiallyinhibit any portion of the first metallic layer from mixing with anyportion of the second metallic layer, and etching a same pattern in thesecond metallic layer, the diffusion barrier, and the first metalliclayer.

Another embodiment disclosed herein includes an interferometricmodulator produced by the above process.

Another embodiment disclosed herein includes a method of manufacturing amovable electrode in a MEMS device having a desired tensile stress,including determining a desired tensile stress or range of tensilestress for the movable electrode, forming one or more layers comprisinga material having tensile stress, and forming one or more layerscomprising a material having compressive stress adjacent to the tensilestress materials, whereby combination of the tensile stress of thecompressive stress provide the desired tensile stress or range oftensile stress for the movable electrode.

Another embodiment disclosed herein includes a MEMS device movableelectrode produced by the above process.

Another embodiment disclosed herein includes a method of actuating aMEMS structure, comprising applying an electric field to a mechanicalmembrane in the MEMS structure such that the mechanical membrane movesin response to the electric field, wherein the mechanical membraneincludes a first layer of material, a second layer of material, and adiffusion barrier layer positioned between the first layer and thesecond layer, wherein the diffusion barrier layer is adapted tosubstantially inhibit any portion of the first layer from mixing withany portion of the second layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIG. 5A illustrates one exemplary frame of display data in the 3×3interferometric modulator display of FIG. 2.

FIG. 5B illustrates one exemplary timing diagram for row and columnsignals that may be used to write the frame of FIG. 5A.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 8 is a cross section of an interferometric modulator prior torelease etch.

FIG. 9A is a cross section of an interferometric modulator prior torelease containing a diffusion barrier layer.

FIG. 9B is a cross section of an interferometric modulator containing adiffusion barrier layer after release etching.

FIG. 10 is a flow chart illustrating a process for manufacture of a MEMSstructure with a diffusion barrier layer.

FIG. 11 is a flow chart illustrating a process for tailoring tensilestress in a composite MEMS structure.

FIG. 12 is a micrograph of the process side of an interferometricmodulator having an Al/Cr movable reflective layer.

FIG. 13A is a micrograph of the process side of an interferometricmodulator having an Al/SiO₂/Cr movable reflective layer.

FIG. 13B is a micrograph of the glass side of the interferometricmodulator of FIG. 13A.

FIG. 14A is a micrograph of the interferometric modulator of FIGS. 13Aand 13B in an unactuated state.

FIG. 14B is a micrograph of the interferometric modulator of FIGS. 13Aand 13B in an actuated state.

FIG. 15A is a micrograph of another interferometric modulator having anAl/SiO₂/Cr movable reflective layer at 50× magnification.

FIG. 15B is a micrograph of the interferometric modulator of FIG. 15A at200× magnification.

FIG. 16A is a micrograph of the interferometric modulator of FIGS. 15Aand 15B in an unactuated state.

FIG. 16B is a micrograph of the interferometric modulator of FIGS. 15Aand 15B in an actuated state.

FIG. 17 is a graph of the optical response as a function of voltage ofthe interferometric modulator of FIGS. 15A and 15B.

FIG. 18A is a micrograph of another interferometric modulator having anAl/SiO₂/Cr movable reflective layer prior to release etch.

FIG. 18B is a micrograph of the interferometric modulator of FIG. 18Aafter release etch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

In many MEMS devices, structures are formed having metallic layersadjacent to each other. These adjacent layers can present uniqueproblems, such as mixing of the metals at their interface to createmetal alloys. Such alloys can alter the physical characteristics of thestructure. In addition, the alloys may complicate manufacturing sincethey do not respond to etchants in the same way that the pure metals do.Accordingly, in some embodiments described herein, a diffusion barrierlayer is used to prevent metallic interdiffusion and therefore to expandand improve the utilization of composite metallic layers in MEMSdevices. In an illustrated embodiment, the diffusion barrier is betweena mechanical layer and a reflective layer in an interferometricmodulator, particularly between a chromium mechanical layer and analuminum reflective layer.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. The partially reflective layer can be formedfrom a variety of materials that are partially reflective such asvarious metals, semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials.

In some embodiments, the layers of the optical stack are patterned intoparallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5B illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4, 5A, and 5B illustrate one possible actuation protocol forcreating a display frame on the 3×3 array of FIG. 2. FIG. 4 illustratesa possible set of column and row voltage levels that may be used forpixels exhibiting the hysteresis curves of FIG. 3. In the FIG. 4embodiment, actuating a pixel involves setting the appropriate column to−V_(bias), and the appropriate row to +ΔV, which may correspond to −5volts and +5 volts respectively Relaxing the pixel is accomplished bysetting the appropriate column to +V_(bias), and the appropriate row tothe same +ΔV, producing a zero volt potential difference across thepixel. In those rows where the row voltage is held at zero volts, thepixels are stable in whatever state they were originally in, regardlessof whether the column is at +V_(bias), or −V_(bias). As is alsoillustrated in FIG. 4, it will be appreciated that voltages of oppositepolarity than those described above can be used, e.g., actuating a pixelcan involve setting the appropriate column to ±V_(bias), and theappropriate row to −ΔV. In this embodiment, releasing the pixel isaccomplished by setting the appropriate column to −V_(bias), and theappropriate row to the same −ΔV, producing a zero volt potentialdifference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 44, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of the exemplary display device 40 may be any of avariety of displays, including a bi-stable display, as described herein.In other embodiments, the display 30 includes a flat-panel display, suchas plasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g., filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28, and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one or moredevices over a network. In one embodiment the network interface 27 mayalso have some processing capabilities to relieve requirements of theprocessor 21. The antenna 43 is any antenna known to those of skill inthe art for transmitting and receiving signals. In one embodiment, theantenna transmits and receives RF signals according to the IEEE 802.11standard, including IEEE 802.11(a), (b), or (g). In another embodiment,the antenna transmits and receives RF signals according to the BLUETOOTHstandard. In the case of a cellular telephone, the antenna is designedto receive CDMA, GSM, AMPS or other known signals that are used tocommunicate within a wireless cell phone network. The transceiver 47pre-processes the signals received from the antenna 43 so that they maybe received by and further manipulated by the processor 21. Thetransceiver 47 also processes signals received from the processor 21 sothat they may be transmitted from the exemplary display device 40 viathe antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, the network interface27 can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

The processor 21 generally controls the overall operation of theexemplary display device 40. The processor 21 receives data, such ascompressed image data from the network interface 27 or an image source,and processes the data into raw image data or into a format that isreadily processed into raw image data. The processor 21 then sends theprocessed data to the driver controller 29 or to the frame buffer 28 forstorage. Raw data typically refers to the information that identifiesthe image characteristics at each location within an image. For example,such image characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40. Theconditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. The conditioning hardware 52 may be discretecomponents within the exemplary display device 40, or may beincorporated within the processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, the driver controller29 is a conventional display controller or a bi-stable displaycontroller (e.g., an interferometric modulator controller). In anotherembodiment, the array driver 22 is a conventional driver or a bi-stabledisplay driver (e.g., an interferometric modulator display). In oneembodiment, the driver controller 29 is integrated with the array driver22. Such an embodiment is common in highly integrated systems such ascellular phones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, the input device 48includes a keypad, such as a QWERTY keyboard or a telephone keypad, abutton, a switch, a touch-sensitive screen, a pressure- orheat-sensitive membrane. In one embodiment, the microphone 46 is aninput device for the exemplary display device 40. When the microphone 46is used to input data to the device, voice commands may be provided by auser for controlling operations of the exemplary display device 40.

The power supply 50 can include a variety of energy storage devices asare well known in the art. For example, in one embodiment, the powersupply 50 is a rechargeable battery, such as a nickel-cadmium battery ora lithium ion battery. In another embodiment, the power supply 50 is arenewable energy source, a capacitor, or a solar cell, including aplastic solar cell, and solar-cell paint. In another embodiment, thepower supply 50 is configured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. Those of skill in the art will recognizethat the above-described optimization may be implemented in any numberof hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports 18 at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. The connections are herein referred to as supports or posts18. The embodiment illustrated in FIG. 7D has supports 18 includingsupport post plugs 42 upon which the deformable layer 34 rests. Themovable reflective layer 14 remains suspended over the cavity, as inFIGS. 7A-7C, but the deformable layer 34 does not form the support postsby filling holes between the deformable layer 34 and the optical stack16. Rather, the support posts 18 are formed of a planarization material,which is used to form support post plugs 42. The embodiment illustratedin FIG. 7E is based on the embodiment shown in FIG. 7D, but may also beadapted to work with any of the embodiments illustrated in FIGS. 7A-7Cas well as additional embodiments not shown. In the embodiment shown inFIG. 7E, an extra layer of metal or other conductive material has beenused to form a bus structure 44. This allows signal routing along theback of the interferometric modulators, eliminating a number ofelectrodes that may otherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIGS. 7A-7E, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields the portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34. This allows theshielded areas to be configured and operated upon without negativelyaffecting the image quality. Such shielding allows the bus structure 44in FIG. 7E, which provides the ability to separate the opticalproperties of the modulator from the electromechanical properties of themodulator, such as addressing and the movements that result from thataddressing. This separable modulator architecture allows the structuraldesign and materials used for the electromechanical aspects and theoptical aspects of the modulator to be selected and to functionindependently of each other. Moreover, the embodiments shown in FIGS.7C-7E have additional benefits deriving from the decoupling of theoptical properties of the reflective layer 14 from the mechanicalproperties of the modulator, which are carried out by the deformablelayer 34. This allows the structural design and materials used for thereflective layer 14 to be optimized with respect to the opticalproperties, and the structural design and materials used for thedeformable layer 34 to be optimized with respect to desired mechanicalproperties.

The interferometric modulators described above may be manufactured usingany suitable manufacturing techniques known in the art for making MEMSdevices. For example, the various material layers making up theinterferometric modulators may be sequentially deposited onto atransparent substrate with appropriate patterning and etching stepsconducted between deposition steps. Because materials in theinterferometric modulators are deposited adjacent to each other,interaction can occur between the materials. In some cases, thisinteraction has negative effects on the manufacturing and/or theproperties of the final device. For example, formation of alloys orcompounds due to the interaction of two layers can cause incompleteetching because the etchants used may not be effective at removing thealloy or compound. In addition, the formation of unintended alloys orcompounds may alter the physical characteristics of the layers, such asby altering tensile stress.

In some embodiments, multiple layers may be deposited duringinterferometric modulator manufacturing without any etching stepsbetween the deposition steps. For example, the movable reflective layerdescribed above may consist of a composite structure having two or morelayers. In one embodiment, one layer provides high reflectivitycharacteristics while the second layer provides a mechanical support forthe reflective layer. The composition and thicknesses of the layersdetermine the tensile stress present in the movable reflective layer. Ifthe tensile stress is too low, the movable reflective layer may sag whenin the relaxed state and may not rebound well after actuation. If thetensile stress is too high, the movable reflective layer may not actuateor may delaminate or buckle during manufacture. The composition andthicknesses of the layers also affect the robustness of the movablereflective layer.

One interferometric modulator design utilizing a composite movablereflective layer is depicted in FIG. 8. During manufacturing, a layer ofindium-tin-oxide (ITO) 154 is deposited onto a transparent substrate152. The ITO 154, which is a transparent conductor, provides aconductive plate so that a voltage can be applied between the movablereflective layer in the interferometric modulator and the plate. In oneembodiment, the ITO is about 500 Å thick. Next, a layer of chrome 150 isdeposited. In one embodiment, the chrome 150 is relatively thin (e.g.,preferably between about 50 Å and 150 Å, in one embodiment, 70 Å),allowing it to act as a partial reflector. Alternatively, the chromelayer 150 may be deposited onto the substrate 152 followed by the ITOlayer 154. Next, a dielectric layer 156/158 is deposited. The dielectriclayer may consist of one or more oxides. In some embodiments, thedielectric layer 156/158 may be a composite layer. For example, arelatively thick layer of SiO₂ 156 (e.g., preferably between 300 Å and600 Å, in one embodiment, approximately 450 Å) may be deposited followedby a thin layer of Al₂O₃ 158 (e.g., preferably between about 50 Å and150 Å, in one embodiment, 70 Å) to protect the SiO₂ 156. In someembodiments, three or more oxide layers may be used (e.g.,Al₂O₃—SiO₂—Al₂O₃). The oxide layer 156/158 provides an insulating layerbetween the movable reflective layer and the chrome 150. The thicknessof the layer determines the interference properties of theinterferometric modulator, particularly when it is in an actuated state.Dielectric sub layers can also be used to act as etch stops duringpatterning or removal of the sacrificial layer (described below) or ascharge trapping layers. The layers described above correspond to theoptical stack 16 described above with respect to FIGS. 1 and 7A-7E.These layers may be patterned and etched to form the rows in aninterferometric modulator display.

In the next step, a sacrificial layer 160 is deposited (e.g., preferablybetween about 1000 Å and 3000 Å, in one embodiment, approximately 2000Å). The sacrificial layer provides a space filling material that can beeasily etched away without affecting the other materials. In oneembodiment, the sacrificial layer 160 is molybdenum. Other examples ofsuitable materials for the sacrificial layer include polysilicon,amorphous silicon, or photoresist. In the last step of manufacturing,the sacrificial layer 160 will be etched away to create an air gapbetween the movable reflective layer and the dielectric layer or stack156,158. Patterning and etching of the sacrificial layer 160 may be usedto create holes and trenches in the layer for the formation of posts andrails that will support the movable reflective layer. Planar material162 may be applied to fill the holes and form the posts. Finally, themovable reflective layer 164/166 is formed. In one embodiment, themovable reflective layer 14 is formed. In one embodiment, the movablereflective layer 14 includes a reflective layer 164 and a mechanicallayer 166 supporting the reflective layer 164. In one embodiment, thereflective layer 164 is an aluminum layer (e.g., preferably betweenabout 300 Å and about 1500 Å thick, in one embodiment, approximately 500Å) and the mechanical layer 166 is a nickel layer (e.g., preferablybetween about 500 Å and about 2000 Å, in one embodiment, approximately1450 Å). In some embodiments, an additional aluminum layer is added ontop of the nickel layer 166 to provide better adhesion of photoresistused during patterning. The movable reflective layer 14 may be patternedand etched to form the columns in an interferometric modulator display.

After etching away the sacrificial layer 160 in the structure depictedin FIG. 8, an interferometric modulator similar to that depicted in FIG.7A is obtained. In some embodiments, a dark mask layer may be added tothe transparent substrate 152 prior to addition of the other layers. Thedark mask layer may be patterned to reduce reflection from portions ofthe structure such as posts or rails. In some embodiments, the dark masklayer includes a MoCr layer and an oxide layer. Those of skill in theart will appreciate that patterning and etching steps in addition tothose mentioned here may be used to form an interferometric modulator.Furthermore, it will be appreciated that other structures ofinterferometric modulators are possible, as for example depicted inFIGS. 7B-7E.

As noted above, in some embodiments the movable reflective layerconsists of a reflective layer 164 and a mechanical layer 166. In oneembodiment, a mechanical layer 166 is chosen to have a higher Young'smodulus than the reflective layer 164, thus enhancing the mechanicalproperties of the composite movable reflective layer 14. For example,nickel has a higher Young's modulus than aluminum. However, nickel isnot commonly used in the foundry processes typically found in MEMS andliquid crystal display (LCD) manufacturing facilities. Accordingly, useof nickel in interferometric modulators increases the expense for massproduction of interferometric modulator based displays. An alternativeto nickel for the mechanical support is chromium, which also has ahigher Young's modulus than aluminum. Chromium is a standard materialused in typical foundry processes. However, during deposition ofchromium onto the aluminum layer, chromium and aluminum mix to form analloy at their interface. Alloy formation between aluminum and chromium,as well as between other metallic materials, may occur due to effectssuch as the galvanic effect (diffusion of atoms due to a difference inelectropotential), thermal migration (e.g., during hot depositionprocesses), and electro-migration (e.g., migration caused by applicationof an electric field). The formation of an alloy can create problemsduring manufacturing. For example, the alloy may not be sensitive to theetchant used to etch the two separate metals. In the case of Al—Cr,neither the CR14 used to etch chromium nor PAN used to etch aluminum iseffective at completely etching Al—Cr alloy. In addition, alloyformation can alter the mechanical properties of the composite structurein an undesirable way.

Accordingly, provided herein are diffusion barriers disposed between twolayers to prevent substantial diffusion between the two layers. Forexample, the barrier may be positioned between the reflective andmechanical support layers in an interferometric modulator array movablereflective layer 14. In some embodiments, one or both of the layersbetween which diffusion is prevented are metallic. As depicted in FIG.9A, the manufacturing described above with respect to FIG. 8 may bealtered so that an additional diffusion barrier layer 170 is depositedin the movable reflective layer 14 between the metallic reflective layer164 and the metallic mechanical support layer 166. FIG. 9B depicts theresulting interferometric modulator structure after the sacrificiallayer 160 has been removed by release etching. The diffusion barrierlayer 170 remains part of the movable reflective layer 14 duringoperation of the interferometric modulator.

In some embodiments, the diffusion barrier layer includes a carbide,nitride, oxide, or boride. Non-limiting examples of suitable materialsinclude silicon dioxide, aluminum oxide, Si₃N₄, titanium nitride,tantalum nitride, silicon carbide, titanium carbide, alumino silicate,and TiB₂. In other embodiments, the diffusion barrier layer includes ametal or metal alloy. Non-limiting examples include titanium, tungsten,titanium-tungsten alloy, silicon, and tantalum. The diffusion barrierlayer may be deposited using any suitable technique known in the art,such as physical vapor deposition, chemical vapor deposition, or sol gelprocessing. The thickness of the diffusion barrier layer may be anythickness suitable for substantially inhibiting interdiffusion ofmaterials on either side of the layer. In one embodiment, the thicknessis preferably greater than about 15 Å, more preferably between about 30angstroms and about 100 angstroms. During processing, an etchant that isactive against the diffusion barrier material may be used toappropriately pattern structures that contain the diffusion barrier. Forexample, when silicon dioxide is used, PAD etchant may be used. When acomposite structure containing a diffusion barrier layer needs to bepatterned, it can be done so with a series of etchants. For example, amovable reflective layer containing aluminum/silicon dioxide/chromiumcan be patterned and etched using sequentially CR14, PAD, and PAN asetchants. During each etching step, the underlying material acts as anetch stop for the etching of the above material. Thus, for example,while etching chromium with CR14, the underlying silicon dioxide acts asan etch stop for the etching of the chromium.

When the diffusion barrier layer is an insulator, either the metallicreflective layer 164 or the metallic mechanical support layer 166 may beconnected to leads for driving an interferometric modulator array. Forexample, voltage applied between the metallic mechanical support layer166 and the ITO 154 layers may be used to cause the entire movablereflective layer 14 to collapse against the dielectric stack 156,158.Alternatively, the voltage may be applied between the metallicreflective layer 164 and the ITO 154 layer.

Thus, in one embodiment, a method is provided for manufacturing a MEMSstructure having at least two metallic layers that includes a diffusionbarrier layer therebetween. FIG. 10 depicts a flowchart for such amethod. At block 200, the first metallic layer is deposited. Forexample, the first metallic layer may be aluminum deposited on thesacrificial layer during interferometric modulator manufacturing. Atblock 202, the diffusion barrier layer is deposited on top of the firstmetallic layer. At block 204, the second metallic layer is deposited ontop of the diffusion barrier layer. Next, the three layers are patternedand etched. In one embodiment, three different etchants are used and thethree layers are sequentially etched. For example, at block 206, thesecond metallic layer may be etched with a first etchant. Next, at block208 the diffusion barrier layer may be etched with a second etchant.Finally, at block 210, the first metallic layer may be etched with athird etchant. The same pattern may applied to all three layers duringetching. For example, a single layer of photo resist may be applied tothe second metallic layer followed by exposure to a single pattern.Sequential etching after developing the photo resist will cause the samepattern to be etched in all three layers. After the second metalliclayer is etched, it can also act as a hard mask during etching of thediffusion barrier layer. Similarly, after the diffusion barrier isetched, it can act as a hard mask during etching of the first metalliclayer. Depending on the particular embodiment, steps may be added tothose depicted in the flowcharts presented herein or some steps may beremoved. In addition, the order of steps may be rearranged depending onthe application.

Although the diffusion barrier layer has been described above for usebetween aluminum and chromium, it will be appreciated that it may beadvantageously employed between any two materials that have thepotential to mix at their interface. For example, non-limiting examplesof materials other than chromium that potentially mix with aluminuminclude titanium, copper, iron, silicon, manganese, magnesium, lithium,silver, gold, nickel, tantalum, and tungsten.

It will also be appreciated that the diffusion barrier layers describedherein may be used in MEMS structures other than the interferometricmodulator movable reflective layers described above. In general, such adiffusion barrier layer may be employed between any two metallic layersin a MEMS device. For example, many mechanical membranes in MEMS devicesmay require composite layers, such as in the movable reflective layerdescribed above. The use of a diffusion barrier layer expands the numberof metals that may be used in composite mechanical membranes. Thebarrier layer may be particularly useful when a composite structure isneeded and it is important that the individual materials have separateproperties, for example where one material requires certain opticalproperties and the other requires certain mechanical and/or electricalproperties.

It will also be appreciated that in some embodiments, as for exampledescribed above, the diffusion barrier layer may act as an etch stopduring MEMS manufacture. In addition to acting as an etch stop forchromium in an aluminum/silicon dioxide/chromium movable reflectivelayer, the diffusion barrier layers described herein can also bedeposited between a sacrificial layer and the movable reflective layerduring manufacture of an interferometric modulator. The diffusionbarrier layer in this example both prevents interdiffusion between thesacrificial layer material (e.g., molybdenum) and the adjacent materialin the movable reflective layer (e.g., aluminum), thereby protecting thesacrificial layer during etching of the adjacent material in the movablereflective layer.

In some embodiments, a composite MEMS structure is provided having twometallic layers with a diffusion barrier layer therebetween as describedabove. In some embodiments, the thicknesses of all three materials arechosen to optimize the desired physical properties of the compositestructure. Physical properties that may be considered include, but arenot limited to, optical properties, electrical properties, thermalproperties, and mechanical properties. For example, it may be desirablethat a mechanical membrane have a specified tensile stress so that ithas certain desired mechanical properties as well as survives themanufacturing process. The examples of metallic layers described hereinincreases tensile stress, while the diffusion barrier materialsdescribed herein, which are characterized by predominantly compressivestress and have a higher modulus of elasticity, decreases tensilestress. Accordingly, in some embodiments, a method is provided forobtaining a mechanical membrane in a MEMS device having a desiredtensile stress.

FIG. 11 depicts a flow chart for one such method. At block 248, adesired tensile stress or range of tensile stress is pre-determinedbased on the particular application of the mechanical membrane. At block250, the thickness of a first material having tensile stress is selected(e.g., a metallic material) based at least in part on the pre-determinedoverall tensile stress desired for the mechanical membrane. At block252, the thickness of a second material having compressive stress isselected (e.g., a diffusion barrier material) based at least in part onthe pre-determined overall tensile stress desired for the mechanicalmembrane. Next, at block 254, a layer of the first material is formed.Finally, at block 256, a layer of the second material is formed adjacentto the first material. The combination of the tensile stress in thefirst material and the compressive stress in the second material givesrise to a combined tensile stress for the mechanical membrane. It willbe appreciated that additional layers having tensile stress orcompressive stress may be added. For example, when the compressivestress material is also acting as a diffusion barrier, three layers maybe included as described above.

In some embodiments, an interferometric modulator movable reflectivelayer is provided that consists of an aluminum-silicon dioxide-chromiumcomposite structure. In some embodiments, the silicon dioxide has athickness of preferably at least about 15 angstroms, more preferablybetween about 30 angstroms and about 100 angstroms. In some embodiments,the thickness of the aluminum layer is preferably between about 200angstroms and about 2000 angstroms, more preferably between about 800angstroms and about 1200 angstroms. In some embodiments, the thicknessof the chromium layer is preferably between about 80 angstroms and about1000 angstroms, more preferably between about 100 angstroms and about500 angstroms.

EXAMPLES Example 1 Measurements of Residual Stress

Several film stacks containing various thicknesses of aluminum andchromium, with and without a silicon dioxide diffusion barrier, weredeposited onto a p type silicon monitor wafer. The curvature of thesilicon wafer was measured before and after deposition using laserreflectance. This curvature was used with the Stoney equation to providea measurement of residual stress in the film stacks. The film stackswere deposited using a MRC 693 sputtering system. Table 1 lists thevarious film stacks manufactured and the resulting residual stress. Forcomparison, a nominal Al (300 Å)/Ni (1000 Å) film stack was found tohave an average residual stress between about 250 and 300 MPa.

TABLE 1 Residual stress of Al/Cr film stacks. Wafer Average measured IDFilm stacks tensile stress (MPa) 111-3 Al(1000 Å)/Cr(200 Å) 220 111-6Al(1500 Å)/Cr(350 Å) 130 111-8 Al(1000 Å)/SiO₂(20 Å)/Cr(200 Å) 125111-10 Al(1000 Å)/SiO₂(20 Å)/Cr(100 Å) 80 103-4 Al(1000 Å)/SiO₂(40Å)/Cr(150 Å) 120  71-7 Al(1000 Å)/SiO₂(40 Å)/Cr(850 Å) 245

It was seen that thicker chromium films increased the tensile stress ofthe film stacks. Furthermore, a separate experiment indicated that theresidual stress of a 1000 Å aluminum film was 10 MPa and a 350 Å silicondioxide film was −123 MPa. Accordingly, these experiments demonstratethat adjusting the silicon dioxide and chromium thicknesses can be usedto tailor the residual stress of mechanical layers containingAl/SiO₂/Cr. In one embodiment the preferred tensile stress for themovable reflective layer in an interferometric modulator is betweenabout 100 MPa and about 500 MPa, more preferably between about 300 MPaand about 500 MPa, and most preferably about 350 MPa.

Example 2 Manufacture of Interferometric Modulators Containing aDiffusion Barrier

The film stacks described in Example 1 were used to manufacture movablereflective layers in an interferometric modulator array. The film stackswere deposited using a MRC 693 sputtering system on 1.1.4+ monochromeglass wafers after deposition of the optical stack, molybdenumsacrificial layer, and deposition of planarization material. The movablereflective layer film stacks were patterned and etched usingsequentially CR14, PAD, and PAN etchants. In the stacks lacking silicondioxide, the PAD etchant was excluded. The molybdenum sacrificial layerwas removed with a dry XeF₂ release etch in 2 cycles with 120 secondsfill time and 300 seconds dwell time. Table 2 indicates the movablereflective layer etchants used on each wafer.

TABLE 2 Interferometric modulator movable reflective layer etchantsWafer ID Film stacks Etchants 111-3 Al(1000 Å)/Cr(200 Å) CR14 (25 s) +PAN (258 s) 111-6 Al(1500 Å)/Cr(350 Å) CR14 (33 s) + PAN (351 s) 111-8Al(1000 Å)/SiO₂(20 Å)/ CR14 (65 s) + PAD (10 s) + Cr(200 Å) PAN (165 s)111-10 Al(1000 Å)/SiO₂(20 Å)/ CR14 (26 s) + PAD (10 s) + Cr(100 Å) PAN(165 s) 103-4 Al(1000 Å)/SiO₂(40 Å)/ CR14 (26 s) + PAD (4 s) + Cr(150 Å)PAN (165 s)  71-7 Al(1000 Å)/SiO₂(40 Å)/ CR14 (84 s) + PAD (4 s) +Cr(850 Å) PAN (165 s)

The etching of the interferometric modulators containing aluminum andchromium without the silicon dioxide diffusion barrier was notsuccessful. FIG. 12 depicts a micrograph of wafer 111-6 from the processside. The large circular patterns 300 indicate that the attemptedetching to form etch holes (for entry of XeF₂ during the release etch)was not complete. In addition, the cuts 302 in the movable reflectivelayer to form columns were not well defined. The incomplete etching wasattributed to the formation of AlCr alloy during processing, causing thesequential etch to be incomplete because CR14 is only effective on purechromium and not AlCr alloy.

In contrast, including a thin film of silicon dioxide between thealuminum and chromium layers improved the etching. When 20 Å of silicondioxide was included, etching was improved; however, higher chromiumetching time (about twice as long as normal) was required and theetching of wafer 111-10 was not successful. FIG. 13A depicts amicrograph of wafer 111-8 from the process side, demonstrating goodformation of etch holes 300 and column cuts 302. FIG. 13B is amicrograph of wafer 111-8 from the glass side. There seemed to be somesagging in the movable reflective layer as observed by a shift from theexpected green color (pixels 304) to blue (pixels 306) in some of theinterferometric modulators. FIGS. 14A and 14B compare wafer 111-8 priorto and after applying a 10V actuation potential, indicating that achange from a bright state to a dark state was observed. However, themovable reflective layer did not rebound after removing the appliedpotential, indicating high stiction or insufficient tensile stress.

Results were improved further by using a 40 Å silicon dioxide layer. Theetching of wafer 103-4 was very successful. FIGS. 15A and 15B aremicrographs depicting wafer 103-4 from the glass side at 50× (FIG. 14A)and 200× (FIG. 14B) magnification. FIGS. 16A and 16B compare wafer 103-4prior to and after applying an 8V actuation potential, indicating that achange from a bright state to a dark state was observed. Furthermore,the movable reflective layer rebounded upon removal of the 8V actuationpotential indicating low stiction was present. FIG. 17 depicts theoptical response as a function of potential measured for wafer 103-4.Although no significant hysteresis was observed, the response wassymmetric and consistent.

In wafer 71-7, the thickness of the chromium was significantlyincreased. FIG. 18A is a micrograph of this wafer prior to the releaseetch. The micrograph indicates good etching of the movable reflectivelayer, with well defined etch holes and column cuts. However, uponapplying the XeF₂ release etch, the movable reflective layer fracturedand collapsed as depicted in the micrograph in FIG. 18B. Accordingly,increasing the tensile stress by too much resulted in a damaged wafer.While not being bound to any particular theory, it is believed thatfurther optimizing the tensile stress, such as by optimizing the silicondioxide and chromium thicknesses, would likely provide improvedhysteresis characteristics without resulting in damage to the movablereflective layer.

Although the invention has been described with reference to embodimentsand examples, it should be understood that numerous and variousmodifications can be made without departing from the spirit of theinvention. Accordingly, the invention is limited only by the followingclaims.

1. A method of manufacturing an interferometric modulator, comprising:depositing a silicon layer; depositing a diffusion barrier layer ontothe silicon layer; depositing a metallic layer comprising a metal ontothe diffusion barrier layer, wherein the diffusion barrier layer isadapted to substantially inhibit any portion of the silicon layer frommixing with any portion of the metallic layer; and etching the siliconlayer using an etchant capable of etching the silicon but not an alloyof silicon and the metal.
 2. The method of claim 1, wherein thediffusion barrier layer comprises an oxide, nitride, or carbide.
 3. Themethod of claim 1, wherein the diffusion barrier layer comprises silicondioxide.
 4. The method of claim 1, wherein the metal includes aluminum.5. The method of claim 1, wherein the silicon layer includes amorphoussilicon.
 6. The method of claim 1, wherein the etchant comprises XeF₂.7. An interferometric modulator produced by the process of claim 1.